1. Field of the Invention
The present invention relates to a substrate processing apparatus to improve roughness caused on a surface of a resist film formed over a substrate such as a semiconductor wafer.
2. Description of the Related Art
In general, photolithography steps in a process to manufacture a semiconductor device include, for example, a resist application process to form a resist film by applying a resist solution over a base film of a semiconductor wafer (hereinafter called a wafer), an exposure process to expose a predetermined circuit pattern on a surface of the wafer, a development process to develop the exposed wafer with a developer, an etching process to etch the base film of the wafer and the like.
After the aforementioned development process, plural striations appear in horizontal and vertical directions on side surfaces, and depressions and projections (LWR (Line Width Roughness) and LER (Line Edge Roughness)) appear on a surface of a resist pattern R as shown in FIG. 14 due to a wave property of light (for example, wavelengths of KrF and ArF are 248 nm and 193 nm respectively) emitted onto the surface of the wafer in the exposure process. When etching the base film by using a mask of the resist pattern R having a rough surface caused by the projections and depressions, projections and depressions such as striations reflecting the striations of the resist pattern R also appear on the base film. As a result, a precise circuit pattern cannot be formed, which degrades a quality of a manufactured semiconductor device.
As a method to improve the aforementioned depressions and projections (LWR (Line Width Roughness) and LER (Line Edge Roughness)), there is disclosed a method (smoothing process) by the present applicant (for example, Patent Document 1) to smooth a top surface of a resist pattern by dissolving the top surface using solvent vapor of a resist (see Patent Document 1).
This smoothing process method employs a scanning method in which a nozzle N provided to face a surface of a substrate such as a wafer W held on a substrate holding stage (not shown) is moved in parallel with the wafer W and solvent vapor is discharged from a discharge hole Na which is provided in the nozzle N to be longer than a diameter of the wafer W, onto the surface of the wafer W which underwent exposure and development as shown in FIGS. 12 and 13. As a result, the resist pattern swells and the depressions and projections caused on the surface of the resist pattern are smoothed.    [Patent Document 1] Japanese Patent Application Publication No. 2005-19969 (claims, FIGS. 4 and 5)
In the scanning method disclosed in Patent Document 1, however, the discharge hole is longer than the diameter of the wafer W. Therefore, the solvent vapor is discharged in areas A where the wafer W does not exist as shown in FIG. 13, which results in wasting the solvent. When smoothing a pattern with a high aspect ratio, a pattern of holes, and the like in particular, the amount of solution is required to be increased to apply an impact pressure. Thus, the waste of the solvent is of concern again.
Moreover, to prevent a solvent vapor atmosphere from diffusing inside the apparatus, safety measures are required, such as sealing up the smoothing process apparatus (module), controlling exhaust of air, and forming an explosion proof structure.